1. Field of the Invention
The present invention relates generally to a background picture display apparatus and an external storage unit used therefor. More particularly, the present invention relates to a background picture display apparatus requiring that a variety of background screens are displayed, such as a television game set, and an external storage unit used therefor.
2. Description of the Prior Art
An example of a picture display apparatus for displaying a background picture in a text system and displaying the background picture and a moving picture in combination is disclosed in Japanese Patent Publication No. 7478/1990 (corresponding to U.S. Pat. No. 4,824,106).
In the above described prior art, only one background screen can be displayed in one scene (frame). It is conceivable that the prior art is altered so as to display a plurality of background screens in one scene by increasing storage capacity. The amount of data which a microprocessor (CPU) used for picture display can process for a constant time is restricted, and an address space of the microprocessor is also restricted. Accordingly, the number of background screens constituting one scene, the number of cells constituting one background screen, the number of colors usable in each of the background screens, and etc. are naturally restricted. For example, if the number of cells constituting one background screen is increased, the number of colors per dot can be increased, while the number of background screens which can be displayed in one scene is decreased. On the other hand, if the number of cells is decreased, the number of background screens can be increased, while the number of colors per dot is decreased.